package org.apache.lucene.search;

import java.util.BitSet;
import java.io.IOException;

import org.apache.lucene.index.IndexReader;

/**
 * Abstract base class providing a mechanism to restrict searches to a subset
 * of an index.
 */
public abstract class Filter implements java.io.Serializable {
  /**
   * Returns a BitSet with true for documents which should be permitted in
   * search results, and false for those that should not.
   */
  public abstract BitSet bits(IndexReader reader) throws IOException;
}
